(a) Field of the Invention
The present invention relates to a gear train for an automatic transmission used in vehicles. More particularly, the invention relates to a gear train for a 6-forward speed and 1-reverse speed automatic transmission.
(b) Description of the Related Art
Generally, automatic transmission systems for vehicles are provided with a transmission control unit ("TCU") which automatically controls shift ratios according to changes in a running condition of the vehicle.
The typical TCU controls a plurality of friction elements provided in a gear train to either operative or inoperative states to select one of the three essential elements of the planetary gear set (a sun gear, a ring gear and a planet carrier) to be an input element, one to be a reaction element, and one to be an output element, thereby controlling an output number of revolutions.
Particularly, a gear train that can realize a 5-forward speed and a 1-reverse speed comprises a plurality of heavy and large-sized clutches and brakes and a plurality of inoperative friction elements, resulting in deterioration of power and space efficiencies.